Refractory WMoNbVTa high-entropy alloy as a diffusion barrier between a molybdenum substrate and MoSi2 ceramic coating

Coating a MoSi2 ceramic layer on Mo substrates is an excellent strategy to enhance their oxidation resistance at elevated temperatures. Suppressing elemental interdiffusion across the Mo/MoSi2 interface is very important for extending the service life of Mo substrates. The present study attempted to develop a WMoNbVTa high-entropy alloy (HEA) layer as a diffusion barrier at the Mo/MoSi2 interface. A new double-layer WMoNbVTa/MoSi2 coating was fabricated on Mo substrates through a two-step spark plasma sintering (SPS) method. Then, the interdiffusion behaviors of Mo/WMoNbVTa/MoSi2 and Mo/MoSi2 systems at 1200–1500 °C were investigated comparatively. A WMoNbVTa HEA powder with a single body-centered cubic (BCC) structure was prepared through mechanical alloying and the intermediate WMoNbVTa HEA layer was successfully fabricated using the milled HEA powder. After long-term oxidation, two diffusion layers of Mo5Si3 and (WMoNbVTa)5Si3 appeared at the WMoNbVTa/MoSi2 interface, while no apparent diffusion zone was found at the Mo/WMoNbVTa interface. The growth rate of the thickness of the diffusion layer at the Mo/WMoNbVTa/MoSi2 interface was much lower than that at the Mo/MoSi2 interface. The WMoNbVTa HEA layer effectively suppressed the interdiffusion of alloying elements between the Mo substrate and MoSi2 ceramic coating. This is attributed to the sluggish diffusion effect of the WMoNbVTa HEA during high-temperature oxidation. The results suggest that WMoNbVTa HEA can be a suitable diffusion barrier between Mo substrates and MoSi2 ceramic coating.